1/* SPDX-License-Identifier: GPL-2.0 */ 2/* 3 * linux/boot/head.S 4 * 5 * Copyright (C) 1991, 1992, 1993 Linus Torvalds 6 */ 7 8/* 9 * head.S contains the 32-bit startup code. 10 * 11 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where 12 * the page directory will exist. The startup code will be overwritten by 13 * the page directory. [According to comments etc elsewhere on a compressed 14 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC] 15 * 16 * Page 0 is deliberately kept safe, since System Management Mode code in 17 * laptops may need to access the BIOS data stored there. This is also 18 * useful for future device drivers that either access the BIOS via VM86 19 * mode. 20 */ 21 22/* 23 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996 24 */ 25 .text 26 27#include <linux/init.h> 28#include <linux/linkage.h> 29#include <asm/segment.h> 30#include <asm/page_types.h> 31#include <asm/boot.h> 32#include <asm/asm-offsets.h> 33#include <asm/bootparam.h> 34 35/* 36 * The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X 37 * relocation to get the symbol address in PIC. When the compressed x86 38 * kernel isn't built as PIC, the linker optimizes R_386_GOT32X 39 * relocations to their fixed symbol addresses. However, when the 40 * compressed x86 kernel is loaded at a different address, it leads 41 * to the following load failure: 42 * 43 * Failed to allocate space for phdrs 44 * 45 * during the decompression stage. 46 * 47 * If the compressed x86 kernel is relocatable at run-time, it should be 48 * compiled with -fPIE, instead of -fPIC, if possible and should be built as 49 * Position Independent Executable (PIE) so that linker won't optimize 50 * R_386_GOT32X relocation to its fixed symbol address. Older 51 * linkers generate R_386_32 relocations against locally defined symbols, 52 * _bss, _ebss, _got and _egot, in PIE. It isn't wrong, just less 53 * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle 54 * R_386_32 relocations when relocating the kernel. To generate 55 * R_386_RELATIVE relocations, we mark _bss, _ebss, _got and _egot as 56 * hidden: 57 */ 58 .hidden _bss 59 .hidden _ebss 60 .hidden _got 61 .hidden _egot 62 63 __HEAD 64SYM_FUNC_START(startup_32) 65 cld 66 cli 67 68/* 69 * Calculate the delta between where we were compiled to run 70 * at and where we were actually loaded at. This can only be done 71 * with a short local call on x86. Nothing else will tell us what 72 * address we are running at. The reserved chunk of the real-mode 73 * data at 0x1e4 (defined as a scratch field) are used as the stack 74 * for this calculation. Only 4 bytes are needed. 75 */ 76 leal (BP_scratch+4)(%esi), %esp 77 call 1f 781: popl %edx 79 subl $1b, %edx 80 81 /* Load new GDT */ 82 leal gdt(%edx), %eax 83 movl %eax, 2(%eax) 84 lgdt (%eax) 85 86 /* Load segment registers with our descriptors */ 87 movl $__BOOT_DS, %eax 88 movl %eax, %ds 89 movl %eax, %es 90 movl %eax, %fs 91 movl %eax, %gs 92 movl %eax, %ss 93 94/* 95 * %edx contains the address we are loaded at by the boot loader and %ebx 96 * contains the address where we should move the kernel image temporarily 97 * for safe in-place decompression. %ebp contains the address that the kernel 98 * will be decompressed to. 99 */ 100 101#ifdef CONFIG_RELOCATABLE 102 movl %edx, %ebx 103 104#ifdef CONFIG_EFI_STUB 105/* 106 * If we were loaded via the EFI LoadImage service, startup_32() will be at an 107 * offset to the start of the space allocated for the image. efi_pe_entry() will 108 * set up image_offset to tell us where the image actually starts, so that we 109 * can use the full available buffer. 110 * image_offset = startup_32 - image_base 111 * Otherwise image_offset will be zero and has no effect on the calculations. 112 */ 113 subl image_offset(%edx), %ebx 114#endif 115 116 movl BP_kernel_alignment(%esi), %eax 117 decl %eax 118 addl %eax, %ebx 119 notl %eax 120 andl %eax, %ebx 121 cmpl $LOAD_PHYSICAL_ADDR, %ebx 122 jae 1f 123#endif 124 movl $LOAD_PHYSICAL_ADDR, %ebx 1251: 126 127 movl %ebx, %ebp // Save the output address for later 128 /* Target address to relocate to for decompression */ 129 addl BP_init_size(%esi), %ebx 130 subl $_end, %ebx 131 132 /* Set up the stack */ 133 leal boot_stack_end(%ebx), %esp 134 135 /* Zero EFLAGS */ 136 pushl $0 137 popfl 138 139/* 140 * Copy the compressed kernel to the end of our buffer 141 * where decompression in place becomes safe. 142 */ 143 pushl %esi 144 leal (_bss-4)(%edx), %esi 145 leal (_bss-4)(%ebx), %edi 146 movl $(_bss - startup_32), %ecx 147 shrl $2, %ecx 148 std 149 rep movsl 150 cld 151 popl %esi 152 153 /* 154 * The GDT may get overwritten either during the copy we just did or 155 * during extract_kernel below. To avoid any issues, repoint the GDTR 156 * to the new copy of the GDT. 157 */ 158 leal gdt(%ebx), %eax 159 movl %eax, 2(%eax) 160 lgdt (%eax) 161 162/* 163 * Jump to the relocated address. 164 */ 165 leal .Lrelocated(%ebx), %eax 166 jmp *%eax 167SYM_FUNC_END(startup_32) 168 169#ifdef CONFIG_EFI_STUB 170SYM_FUNC_START(efi32_stub_entry) 171SYM_FUNC_START_ALIAS(efi_stub_entry) 172 add $0x4, %esp 173 movl 8(%esp), %esi /* save boot_params pointer */ 174 call efi_main 175 leal startup_32(%eax), %eax 176 jmp *%eax 177SYM_FUNC_END(efi32_stub_entry) 178SYM_FUNC_END_ALIAS(efi_stub_entry) 179#endif 180 181 .text 182SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) 183 184/* 185 * Clear BSS (stack is currently empty) 186 */ 187 xorl %eax, %eax 188 leal _bss(%ebx), %edi 189 leal _ebss(%ebx), %ecx 190 subl %edi, %ecx 191 shrl $2, %ecx 192 rep stosl 193 194/* 195 * Adjust our own GOT 196 */ 197 leal _got(%ebx), %edx 198 leal _egot(%ebx), %ecx 1991: 200 cmpl %ecx, %edx 201 jae 2f 202 addl %ebx, (%edx) 203 addl $4, %edx 204 jmp 1b 2052: 206 207/* 208 * Do the extraction, and jump to the new kernel.. 209 */ 210 /* push arguments for extract_kernel: */ 211 pushl $z_output_len /* decompressed length, end of relocs */ 212 213 pushl %ebp /* output address */ 214 215 pushl $z_input_len /* input_len */ 216 leal input_data(%ebx), %eax 217 pushl %eax /* input_data */ 218 leal boot_heap(%ebx), %eax 219 pushl %eax /* heap area */ 220 pushl %esi /* real mode pointer */ 221 call extract_kernel /* returns kernel location in %eax */ 222 addl $24, %esp 223 224/* 225 * Jump to the extracted kernel. 226 */ 227 xorl %ebx, %ebx 228 jmp *%eax 229SYM_FUNC_END(.Lrelocated) 230 231 .data 232 .balign 8 233SYM_DATA_START_LOCAL(gdt) 234 .word gdt_end - gdt - 1 235 .long 0 236 .word 0 237 .quad 0x0000000000000000 /* Reserved */ 238 .quad 0x00cf9a000000ffff /* __KERNEL_CS */ 239 .quad 0x00cf92000000ffff /* __KERNEL_DS */ 240SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end) 241 242#ifdef CONFIG_EFI_STUB 243SYM_DATA(image_offset, .long 0) 244#endif 245 246/* 247 * Stack and heap for uncompression 248 */ 249 .bss 250 .balign 4 251boot_heap: 252 .fill BOOT_HEAP_SIZE, 1, 0 253boot_stack: 254 .fill BOOT_STACK_SIZE, 1, 0 255boot_stack_end: 256